Analysis and Design of a 1.6–28-GHz Compact Wideband LNA in 90-nm CMOS Using a $\pi$ -Match Input Network

This paper presents a wideband low-noise amplifier (LNA) based on the cascode configuration with resistive feedback. Wideband input-impedance matching was achieved using a shunt-shunt feedback resistor in conjunction with a preceding π -match network, while the wideband gain response was obtained using a post-cascode inductor (L_P), which was inserted between the output of the cascoding transistor and the input of the shunt-shunt resistive feedback network to enhance the gain and suppress noise. Theoretical analysis shows that the frequency response of the power gain, as well as the noise figure (NF), can be described by second-order functions with quality factors or damping ratios as parameters. Implemented in 90-nm CMOS technology, the die area of this wideband LNA is only 0.139 mm² including testing pads. It dissipates 21.6-mW power and achieves S₁₁ below -10 dB, S₂₂ below -10 dB, flat S₂₁ of 9.6 ±1.1 dB, and flat NF of 3.68 ± 0.72 dB over the 1.6-28-GHz band. Besides, excellent input third-order inter-modulation point of +4 dBm is also achieved. The analytical, simulated, and measured results are mutually consistent.